The present invention relates to techniques for generating masking sounds.
There has been generally known the phenomenon where, when you are hearing certain voices or sounds (target sounds) and if there are other voices or sounds (masking sounds) having acoustic characteristics (e.g., frequency characteristics) close to those of the target sounds, the target sounds become difficult to hear. Such a phenomenon is commonly called “masking effect”. The masking effect is based on human auditory or aural characteristics, and it has been known that the masking effect becomes more prominent if the masking sounds are closer in frequency to the target sounds and the masking sounds are higher in sound volume level than the target sounds.
Various acoustic techniques have been proposed, among which are techniques disclosed in Published Japanese Translation of International Patent Application No. 2005-534061 (hereinafter referred to as “Patent Literature 1”) which corresponds to International Application Publication No. WO2004/010627. More specifically, Patent Literature 1 discloses a technique which divides a sound signal into a plurality of segments, rearranges or changes the order of the divided segments to convert the sound into a meaningless sound to thereby generate a masking sound.
With the techniques disclosed in Patent Literature 1, the masking effect would sometimes decrease depending on where a sound stream in question is divided (i.e., on divided points of the sound stream). Namely, if the stream can be divided in such a manner as to separate phonemes included in the stream, each sound can be appropriately scrambled, and thus, a sufficiently high masking effect is attainable. However, if the sound stream is divided every predetermined frame length, phonemes may not be separated at suitable points. Further, if the frame length is set short in order to reliably separate phonemes, a generated masking sound would give an unnatural feeling. Therefore, it has heretofore been difficult to set an appropriate frame length for the masking sound generating purpose.